The brutal means that the Sudanese president has used to keep his country together have instead blown it apart in the most chaotic way possible.

South Sudan is being baptized in blood. On Saturday, July 9, when the south formally declares its independence from Sudan, civilians in the disputed border region of Southern Kordofan will be scrambling to survive a sustained campaign of aerial bombardment. A report by an aid worker in the Nuba Mountains of Southern Kordofan described a campaign of "ethnic cleansing" carried out by "troops, artillery, tanks, and machine gun carriers" as well as Antonov bombers. Since Khartoum has blocked the United Nations, NGOs, and the media from the region, it is impossible to know how many civilians have been killed in recent weeks, though aid workers cited in the New York Times put the number at "hundreds." And hundreds more were killed last month in Abyei, another border state.

You might think that Sudanese President Omar Hassan al-Bashir, who has been indicted by the International Criminal Court for carrying out genocide in the western region of Darfur, has decided to violently nullify the January referendum in which the people of the south voted overwhelmingly for independence. But that’s almost certainly not the case. A recent report by the International Crisis Group speculates that Bashir has launched the onslaught in order to improve his negotiating position on a range of issues between north and south, including the drawing of borders and the division of oil revenues. This is Bashir’s idea of statecraft. As Sudan scholar Gérard Prunier once wrote, the regime’s "policy and political philosophy since it came to power in 1989 has kept verging on genocide in its general treatment of the national question in Sudan."

The essential story of Sudan over the last several decades is the story of the regime against the people. This is, of course, a perfectly familiar African story, but what makes Sudan’s story distinctive is the way a small, homogenous class of riverine Arabs has used massive and barely controlled violence to maintain control over an immense and vastly diverse country. In Darfur, it has succeeded. In the south, it has failed; and on Saturday’s independence day the beleaguered people of the south will explode with euphoria before settling down to face an extremely grim future, for South Sudan will be one of the world’s poorest and least-developed countries.

It did not have to be this way, and a remarkable new book of essay and photographs titled We’ll Make Our Homes Here: Sudan at the Referendum offers a powerful reminder that that is so. Tim McKulka, a staff photographer for the U.N. Mission in Sudan (UNMIS), took the pictures, compiled and edited the essays, and somehow — this may be the most impressive part — persuaded UNMIS itself to publish the book. McKulka’s pictures show Sudan in all its topographical and human variety: deserts, mountains, rivers, and the oil-boom capital of Khartoum; nomadic cattle-herders, Arab traders, and Nuer tribesmen with ritual scarification. Sudan is a vast migratory space — at almost 1 million square miles, the world’s 10th-largest country and the largest in Africa — which tribes have crisscrossed over the centuries, depositing one layer of culture and habits atop another.

The book’s 13 essays, most of them intensely personal and all written by Sudanese, are shot through with nostalgia for this densely layered past and for the vanished ethos of tolerance that allowed such varied peoples to live alongside one another. Leila Aboulela, an author and playwright, recalls the cosmopolitan Khartoum of her childhood in the 1960s: "The city was spacious and languid; close-knit and unconventional; a place to be innovative and adventurous." (Afghans who remember the Kabul of that time describe it in much the same language.) Abdalla Adam Khatir, a Darfuri journalist and activist, describes his days as a university student in the 1970s traveling from the Blue Nile to Port Sudan to the massifs of Kordofan. This act of discovery, he writes, "deepened my commitment to the notion of a Sudanese nation."

There may be some glossing over of ugly realities here. The Sudanese have long been pittted against one another as well as against the state: Nuer tribesmen fight Dinka in the south; nomads fight pastoralists along the border. But politics matter, and those who have controlled Sudan have always used some variant of divide-and-rule. As historian Edward Thomas notes in a prefatory essay, 19th-century Ottoman rulers used the south as a source of slaves for the Egyptian army. British administrators later separated the country into ethnic zones in order to preclude the rise of nationalism. When Britain granted Sudan independence in 1956, the Christian south agreed to join with the Islamic north only on the condition that the country adopt a decentralized system; instead, Britain handed off its full colonial powers to a mercantile Arab regime in Khartoum. A campaign to forcibly Islamize the south provoked a civil war that lasted until a 1972 peace treaty. A new military ruler dissolved the south’s autonomous government, setting off a new round of fighting in 1983. Two million people died before the two sides signed the 2005 agreement that set the stage for this year’s referendum and independence. And as one war was winding down, a new one in Darfur, provoked by the same repressive policies and carried out with the same brutality, was starting up.

I cannot help thinking of India when I read this story. There is an obvious analogy between the bloodshed surrounding the hiving off of south from north and India’s Partition, which led to the deaths of perhaps a quarter-million people as Muslims fled north to Pakistan and Hindus south to India. Sudan is suffering through a partition of its own. But there was nothing inevitable about the fratricide either at India’s birth or at South Sudan’s; both are a consequence of political choices. And in fact what actually strikes me is the contrast between the choices made by the two countries’ post-colonial leaders. India’s prime minister, Jawaharlal Nehru, horrified by the violent energies unleashed by Partition, went to enormous lengths to calm anti-Muslim feeling in India and to blunt calls to redraw state borders along linguistic lines. And when violence flared over the linguistic issue in 1955, Nehru gave in, recognizing that India could survive as a diverse country only by granting more regional and cultural autonomy.

Multiethnic states like Sudan are not doomed to failure. India is just one example; Indonesia is another. It all depends on political leadership. Of course, the problem is harder in diverse states ruled by a minority tribe, such as Sudan or Syria. Leaders must either bring others into the circle of power or practice endless repression. Bashir has made the latter choice; so, too, has the Assad family in Syria. President Bashar al-Assad is now discovering the corollary to this choice: As repression provokes resistance, the regime must keep ratcheting up the level of brutality in order to survive.

If you’re the president of a country as big as Sudan, you can sustain your rule by letting go of a piece of the country you can no longer successfully repress. But you cannot sustain the idea of the country. John Garang, the southern leader who had signed the 2005 agreement with the Bashir regime and died soon thereafter in a plane crash, had fought for the vision of a single Sudan with a mixed leadership. That sounds almost laughably naive today. Jacob J. Akol, a southern journalist, writes in We’ll Make Our Homes Here that while the myth of Sudan is "an Islamic and culturally Arab nation in the heart of Africa," the reality is "a people trying to break away from a forced and unfair unity about which they were never consulted." Nothing but force holds Sudan together.

Leafing through the volume, I was struck by a picture of a giant parabola on Khartoum’s skyline — a new oil company headquarters. That hadn’t been there when I visited in 2004. Oil revenue has made Sudan one of Africa’s fastest-growing states; the fight over the border regions has much to do with access to that oil wealth. But while it will transform Khartoum’s skyline, oil wealth will not solve Sudan’s problems: By increasing corruption and further concentrating wealth and power in the center, it will only further alienate the millions who live along the periphery. Bashir has a genius for survival, and he may outlast his enemies; but Sudan, as a country, will fail.

James Traub is a contributing editor at Foreign Policy, a fellow at the Center on International Cooperation, and author of the book "John Quincy Adams: Militant Spirit." @jamestraub1